> ...
> The place we spent the most time in the 21st century, Afghanistan, somehow went from an objective of destroying Al Qaeda to ensuring that girls got a good education and had equal rights.
I think in Afghanistan's case, the goal was clear but it was not achievable. A bombing campaign, some boots on the ground, and killing some leaders could not actually achieve the "objective of destroying Al Qaeda," because it would just re-form afterwards. You'd have to change the society so it wouldn't reform, hence "ensuring that girls got a good education and had equal rights."
Though I suppose installing and supporting some brutal warlord as a secular dictator (e.g. a Saddam Hussein) would have achieved the objective too, but the US would have gotten so much condemnation for that I'm sure the option was not on the table.